The present invention relates to an inorganic filler, particularly relates to a composition containing an organic polymer material as a matrix, particularly to an inorganic filler which is suitable for using as a filler in a dental composition, and a process for producing the same.
In addition, the present invention relates a multi-functional filler, particularly relates to a composition containing an organic polymer material as a matrix, particularly to an inorganic filler which is suitable for using as a filler in a dental composition, and a process for producing the same.
In addition, the present invention relates to a composition having a resin matrix of an organic polymer material, in particular, an organic compound filler which is suitable for using as a filler in a dental composition, as well as a process for producing the same.
Furthermore, the present invention relates to a composition having a resin matrix of an organic polymer material, in particular, a modified filler which is suitable for using as a filler in a dental composition, as well as a process for producing the same.
Furthermore, the present invention relates to a dental coloring filler which can be used in the dental field such as a crown and bridge material, a filling material, a prosthetic material and an adhesive material, light-shielding material (an opaque material), and a process for producing the same, as well as a dental composition containing the same.
A composite restorative material which is widely used in the dental field in recent years is required to have the following properties. As such there are certain mechanical properties such as the mechanical strength which can stand a high gliding occlusal pressure upon mastication, the durability under severe conditions, the thermal expansion coefficient having the similar magnitude to that of a teeth substance and the low polymerization shrinkage for preventing stripping from a teeth substance upon curing and the like, the optical properties such as the color tone and the transparency adapted to a natural teeth and the surface smoothness and glossiness observed after polishing and the like. In addition to the bio-compatibility such as the non-toxicity, the insolubility and the low water absorbing property and the like. Moreover, particularly recently, the properties such as the sustained fluoride releasability for reinforcing a teeth substance to prevent dental caries and the radiopacity for confirming the recurrence situation of secondary caries after the treatment and for being capable of distinguishing from an enamel of a teeth substance have been required.
Composite restorative materials composed of a polymerizable monomer, a polymerization initiator, and a filler such as an inorganic material, an organic material and an organic-inorganic compound material and the like have hitherto been used for all restoration, such as filling and repairing, of a dentinal defective-part, prosthesis, artificial fang and other uses. Among these components, many have hitherto been reported on a filler. This is because the properties of a filler are thought to have the influence on the properties of a composite restorative material since the filler accounts for a large proportion of the composite restorative material.
Fillers which have used in a composite restorative material at the early stage are mainly a ground-type filler prepared by grinding a large mass such as a xcex1-quartz and a variety of glasses having an average particle size of a few microns to a few hundreds microns. When these fillers are used, they can impart various properties such as the suitable viscosity and the handling, the mechanical strength, the low polymerization shrinkage, the thermal expansion coefficient similar to that of a teeth substance to a composite restorative material.
However, such fillers have unacceptable polishability because of a large average particle size and, in particular, they have the shortcomings such as the inferior surface smoothness and the surface glossiness after polishing. In order to overcome this problem, an attempt has been tried to make an average particle size as small as possible but has not been sufficient yet.
In order to overcome this shortcoming, there has been proposed a composite restorative material using, as a filler, a ultrafme particle having an average particle size of 0.01xcx9c0.1 xcexcm synthesized by a pyrolytic process or a a vapor phase process, for example, spray-pyrolized silica and fumed silica, and these have been used widely as a general abbreviation of MFR. This composite restorative material has the better polishability and is excellent in the surface smoothness and the surface glossiness. However, when the ultrafine particle is dispersed in a polymerizable monomer, the viscosity of the resulting paste is highly increased due to a large specific surface area and, for this reason, an amount of a filler content must be considerably suppressed. For this reason, the mechanical property of a composite restorative material, particularly, the bending strength becomes inferior. In addition, they have also a problem that the polymerization shrinkage upon the curing of a paste is relatively large and, additionally, the thermal expansion coefficient of a cured material becomes very large.
As the other filler, there are silica and silica composite oxide which are synthesized by a solution reaction such as a sol-gel process starting with an organometal compound, are narrow in the particle size distribution, are spherical and have an average particle size of 0.1 xcexcm to a few microns. These fillers are disclosed in JP-A 59-101409 and the like. Since these fillers cause aggregation at a drying step, the surface treatment of a filler can not be performed uniformly and there is a problem on the mechanical strength and the durability such as deterioration of a material due to water absorption.
In addition, in the light of impartation of the favorable nature of each filler, there are provided hybrid-type composite materials in which an ultrafine particle of silica and a relatively large inorganic filler are combined.
For example, they are disclosed in JP-A 57-82303, J-A 57-50150, JP-A 61-148108 and the like. However, although these hybrid types improve the mechanical properties sufficiently, there is a problem that the operability is bad due to a viscous paste and they lack the smoothness after finish polishing as compared with MFR.
Then, for the purpose of satisfying the various properties necessary for a composite restorative material, many attempts have been hitherto reported to perform high density packing by fine-grinding and aggregating techniques and surface treating techniques. For example, a process of obtaining an aggregate from a solution of a metal compound and a silica sol is described in JP-A 7-196428 and a process of aggregating a metal oxide having an average particle size of not smaller than 0.05 xcexcm and not greater than 1 xcexcm is described in JP-A 7-196431. Although these improve the polishability, a surface treating agent such as a silane coupling agent does not act on aggregated parts, which causes a decrease in the durability due to water absorption.
According to the results of the present inventor""s study, in order to obtain a sufficient polishability and mechanical properties such as the durability and the mechanical strength, it was found that the selection of a raw material of an inorganic filler, the fine-grinding and the surface treatment are a very important factor, but a variety of problems resulted. As a process of fine-grinding which has been previously performed, there is a dry-grinding process by a mechanical process with an ocsillating mill, a ball mill, a jet mill and the like. According to this process, it is difficult to obtain a particle having an average particle size of 3 xcexcm or less and, since the particle size distribution is large, a complicated step such as separation becomes necessary. In addition, although in wet-grinding using the facility therefor, grinding can be performed to an extent of an average particle size of 1 xcexcm or less, the aggregation of particles occurs at a drying step. Even when this aggregate was tried to be disintegrated using a suitable disintegrating equipment, it was impossible to disintegrate to primary particles. As another fine-grinding process, there is preparation of fine particles from the solution state using the sol-gel process techniques. However, since a drying step is also necessary for this process, aggregates are produced. It was also found that, since these aggregates do not undergo the uniform surface treatment, when they are used as a filler in a composite restorative material, the durability is problematic. In addition, silica has mainly been used previously as a raw material for an inorganic filler. However, it has problems on the polishability and wear of opposing teeth due to its hardness. For that reason, a variety of raw materials have begun to be used from a viewpoint of the necessity of imparting many properties to an inorganic filler. To the contrary, it was found that the effect of a silane coupling agent, which is generally used, becomes poor and it has the influence on the mechanical strength. In addition, it is contemplated that although the polishability and surface smoothness and glossiness can be improved by fine-grinding, the high density packing into a composite restorative material becomes difficult due to increased specific surface area and the influence on the mechanical strength.
From the foregoing, in order to satisfy the properties required for a composite restorative material, it is an important theme to maintain the particle size control and the uniform monodispersion without any agregation, and it is necessary that the surface is treated uniformly with a surface treating agent.
In general, in the dental field, a silane coupling agent is known as the known surface treating agent. However, this treating agent does not necessarily act effectively on all inorganic fillers. It is effective for an inorganicfiller to have many OH groups on the surface such as silica, but when an amount of OH groups is decreased, its effect is decreased. JP-B 5-67656 describes a polymerizable aromatic carboxylic acid compound for treating the surface of alumina, Japanese Patent No. 2695479 describes a dicarboxylic acid compound as an agent for treating the surface of an inorganic filler, and Japanese Patent No. 2925155 describes an organic phosphorus compound as an agent for treating the surface of an inorganic filler. Like this, since an amount of OH groups on the surface is different depending upon an inorganic filler used, it was necessary to use a variety of surface treating agents depending upon a kind of an inorganic filler to be treated. For this reason, the wettability with a resin is different depending upon a surface treating agent, used for treating the surface of a particle, it may have the adverse influence on the various properties, such as a change in not only the properties of the resulting composite restorative material but also the nature and the handling of a paste before the curing. In addition, JP-B 6-99136 describes two kinds of silane coupling agents, long chain or short chain, and Japanese Patent No. 2690364 describes the surface treatment using a silane coupling agent having a large hydrophobic group, and objects of which are both to improve the surface treatment effect. However, there has not been obtained an inorganic filler which has the sufficient polishability and durability and satisfies other various properties, and which has no aggregate, is monodispersed and has the uniformly treated surface.
Recently, some fillers are proposed, which focus on their optical properties such as the polishability and surface smoothness and glossiness and the like, for example, including a filler which is generally called as an organic-inorganic compound filler or a compound filler. These are made by pre-mixing an inorganic particle with a polymerizable monomer to polymerize once to give a polymer, which is then ground to obtain a compound filler. Although JP-A 54-107187 discloses a compound filler using a ultrafine particle as an inorganic particle, it has a defect that, for example, since the ultrafine particle has a large specific surface area, its proportion in the compound filler is small so that the surface hardness of a composite restorative material containing this compound filler is low and its thermal expansion coefficient becomes high. In addition, composite restorative materials containing: as an inorganic particle, a compound inorganic oxide composed of silica and another element which can bind with the silica which has an average particle size of 0.1xcx9c1.0 xcexcm and is spherical in JP-A 3-12043; as an inorganic particle, a compound oxide composed of silica dioxide and an element of Group IIxcx9cIV in the Periodic Table having an average particle size of 0.01-0.1 xcexcm in JP-A 8-143747; and as an inorganic particle, a glass powder having an average particle size of 0.1xcx9c5.0 xcexcm in JP-A 5-194135 are disclosed, respectively. Although they can solve the problems in the surface hardness and the thermal expansion coefficient by increasing a proportion of the content of inorganic components in the filler, there is almost no improvement in the mechanical properties. Further, a compound filler having the surface on which double bonds are left by using a trifunctional or difunctional polymerizable monomer in JP-B 6-62687; and a compound filler containing an aggregate obtained by aggregating an inorganic particle having an average particle size not greater than 1.0 xcexcm, and heat-treating in JP-A 7-196430, are disclosed, respectively. However, they are aiming at improving their mechanical properties, but the effect is insufficient. Then, for the purpose of improving the mechanical properties, composite restorative materials using a compound filler and another inorganic filler therein are disclosed. JP-B 7-91170 discloses a glass filler, an a ultrafine silica particle and a compound filler, and JP-A 9-194674 discloses a composite restorative material containing a compound filler and an aggregated inorganic oxide particle. However, since these had a shortcoming resulted from the use of inorganic fillers, they were not necessarily satisfactory in all properties required for composite restorative materials.
As mentioned above, the compound filler has the excellent optical properties after polishing, such as the surface smoothness and glossiness and the like, but the effect of the surface treatment on the compound filler is insufficient, and the wettability with a resin component becomes poorer and, therefore, it has a big problem in the mechanical properties or handling. Almost all the components on the surface of the compound filler are organic components and a little amount of inorganic components are present there. In addition, although inorganic components are exposed there, the surfaces of the inorganic particles are already treated by using a silane coupling agent and the like, when the compound filler is produced. Therefore, it is considered that the effect of the surface treatment on the compound filler is not exhibited sufficiently, and the mechanical properties can not be achieved. Further, when the surface treatment is not done uniformly and effectively, the handling of a paste thereof, which is a state before curing, and the durability of the composite restorative material containing the compound filler after curing, and the like are affected. Almost all of the previous surface treatments on a compound filler were within the physical adsorption of a surface treating agent. In the handling of the paste, the wettability between the surface of a filler and a resin matrix is an important factor and, in the case of the physical adsorption, since the surface treating agent is removed from the filler surface with time, the wettability changes, that is, the handling tends to become worse. Additionally, in the cured material thereof, minute gaps are generated in the interface between the filler surface and the resin matrix, and the permeation of water into the gaps makes a problem in the durability and the like. There is no organic compound filler having the excellent polishability, particularly the surface smoothness and glossiness after polishing, which are the conventional features of a compound filler as the above fillers have, and in which the surface treating agent can act effectively to impart the excellent mechanical properties, the durability, and the stable handling.
In the dental field, the effect of fluoride to prevent dental caries is well known. As fluoride-releasing dental materials which have been previously used, there are cement materials known as a glass ionomer cement or a glass polyalkenoate cement. However, since these materials are have poor durability, there are problems on the quality of the materials themselves, such as a change in the color tone and the breakage in a shorter period as short as one year, regardless of their advantage in the ability of the sustained fluoride release. In addition, although the incorporation of a metal fluoride compound such as sodium fluoride to dental materials (JP-A 2-258602) has been attempted, such an attempt had shortcomings that a large amount of fluoride is dissolved out in a shorter period and are not sustained fluoride release, and the mechanical strength of the materials themselves is decreased. Although the incorporation of a polymer comprising an acid fluoride component of acrylic acid or methacrylic acid into a composite restorative material was reported (JP-A 57-8.8106, JP-A 62-12706 and Japanese Patent No. 2678108), there were shortcomings that although fluoride is released at a small quantity over a longer period of time, it can not be applied to sites where a high load is applied, and the effect of fluoride ions can not be expected because it has a low fluoride content due to a little proportion of a resin component in the composite restorative material. JP-A 11-209213 and JP-A 10-36116 report a metal fluoride compound covered with polysiloxane. This is aimed at controlling the release of fluoride by controlling the solubility of metal fluoride, but the metal fluoride can not be incorporated into materials for which the mechanical strength is required, such as composite restorative materials.
In addition, JP-A 7-206470 and JP-A 11-268929 report the release of fluoride from glass materials without the acid treatment, however, this means that the glass itself dissolves in water, resulting in a problem regarding the long term durability. WO94/23687 describes a fluoride sustained release pre-formed glass ionomer filler which is formed from a powder-form reaction product of a polyalkenoic acid and a fluoride-containing glass. This is characterized by the sustained fluoride release without accompanied by no dissolution disintegration. However, since the glass surface of this filler reacts with the polyalkenoic acid, the effect of the surface treatment is not sufficient and there are problems in the mechanical properties and the durability. Moreover, there is no description with respect to the light-diffusion of the transmitted light or the polishability. In addition, recently, a xe2x80x9ccompomerxe2x80x9d is focused on as an in-between material of a glass ionomer cement and a composite resin. This is a one-paste type composition comprising a glass used for a glass ionomer cement and an acidic group-containing monomer, and exhibits the high fluoride releasability, but its mechanical strength is decreased by contact with water for a longer period of time. Thus, dental restorative materials are desired which have the fluoride releasability, and have the stability in water for a longer period of time as well as the mechanical properties to stand a high occlusion pressure.
Amalgams have been previously used for a filling restoration after the treatment of dental caries and gold alloys have been used for crown restoration. In recent years, composite materials have become rapidly prevalent because it is not expensive and is relatively easy to achieve the color tone and the transparency close to those of natural teeth by using them. Now, composite restorative materials are used not only for restoration and prosthesis of odontic defects, but also for applications in an adhesive material, a sealant, an artificial fang and the like. Recently, among various properties of the composite restorative materials, the aesthetic properties such as the polishability, the surface smoothness and glossiness after polishing, the transparency, and the color tone are required at a high level by clinician""s needs. Many reports are proposed on the great contribution of the components of the composite restorative materials to a variety of properties of the material for expressing the aestheticism of the composite restorative materials.
For example, JP-A 11-100305 proposes that the same color tone and texture as those of natural teeth can be obtained by controlling a particle size and a refractive index of a colloidal silica and a refractive index of a polymerizable monomer. In addition, JP-B 745373 proposed that a change in color tones between before and after polymerization can be rendered smaller by inclusion, in a composite material, of both a filler having a refractive index lower than an average value of refractive indexes of a matrix before and after polymerization, and a filler having a refractive index higher than the average value. Further, JP-A 9-255516 proposes that a composite material containing an aggregate of an inorganic filler having the difference in a refractive index from a resin matrix after polymerization of 0.06 or less and having an average particle size of 0.01xcx9c1.0 xcexcm, and an inorganic filler having the difference in a refractive index from a resin matrix after polymerization of more than 0.06 and having an average particle size of 1.0 xcexcm or more is excellent in the color tone compatibility and the mechanical properties due to possession of a certain light-diffusion.
In addition, processes for evaluating aesthetic properties of a composite restorative material are reported and, for example, JP-A 7-196429 describes that the transparency of a composite restorative material is evaluated by a contrast ratio, and a site to be applied is decided with the ratio so that an aesthetic and convenient cavity restoration can be carried out.
However, it is insufficient to evaluate the aestheticism only by the above factors. For example, a problem occurred that since the light transmission of the cured product becomes very strong as a filler becomes finer, when natural teeth are restored, the incongruity becomes very strong depending upon the background color, a material and a direction of the observation.
JP-A 9-169613 proposes that as evaluation of the optical properties close. to those of natural teeth, from the distribution state of the light having transmitted through a composite restorative material, the distribution of transmitted light is numerically processed by using the diffusion factor (D).
Additionally, the dental compositions using the previous filler exhibited the unsatisfactory results, since when such the dental composition was filled as a restorative material or a prosthetic material, the unevenness of the diffusion light intensity due to the poor light diffusivity of a filler resulted in that, for example, the color tone varies depending upon a direction of observation and, consequently, the effect of color matching exhibited insufficiently.
In order to endow a composite restorative material with the excellent aestheticism, technical factors are in deed required, such as, control of refractive indices of a filler and a polymerizable monomer aiming at endowing with the transparency close to that of natural teeth, the fine-grinding of a filler aiming at endowing with the properties such as the polishability, the surface smoothrness glossiness after polishing, the impartation of the transmittance and the diffusion of the light in the interior of a composite restorative material aiming at reducing the effect of the background color and the dependency of the color tone on an observation angle, and the like. However, it is insufficient to evaluate the aestheticism only with these properties, and it is also essentially an important factor for expressing the aestheticism that the composite restorative-material has the color tone very close to that of natural teeth.
In the dental field, the impartation of the color tone to a dental composition such as a crown and bridge material, a filling material, a prosthetic material, an adhesive material, and a light-shielding material (opaque material), that is, the toning has hitherto been carried out by using a process of adding a pigment as it is or a process of diluting a pigment with components of a dental composition such as a polymerizable monomer and a filler to prepare a diluted pigment, then adding the diluted pigment (a master batch process). The former has better workability than the latter because the former does not include a step of preparing a diluted pigment. However, since in the toning of a dental composition, an amount of a pigment to be used is so small and there are a wide variety of color tone systems and colors, it is very difficult to finely adjust amounts of pigments. Moreover, a dispersibility is different depending upon, for example, a kind of a pigment and, therefore, the intended color can not be realized. On the other hand, the latter, comparing to the former, has problems in the workability and the cost because a diluted pigment obtained by diluting a pigment is used, and a step of preparing a diluted pigment is added, although a fine adjustment of an amount of a pigment to be added is possible. Moreover, the dispersibility of a pigment is better than the former, but not satisfactory. These toning processes are performed in the final step of preparing any dental compositions, and only mixing the pigments as mentioned above cannot produce the stable color tone and may affect other properties of a dental composition. This is because a pigment particle generally tends to aggregate easily due to a so small particle size and a large specific surface area, and because it is difficult to disperse uniformly due to the different surface characteristic in the compatibility of a pigment fiom those of components for a dental composition such as a polymerizable monomer and a filler, and the like. In addition, since the wettability with a polymerizable monomer and the like varies dependingupon a kind of a pigment to be used, a mixing ratio of a pigment to be used has the effect on characteristics of a dental composition paste. When the toning of a dental composition is actually performed, a polynerizable monomer, a filler, a pigment and the like are kneaded or stirred uniformly, but it is frequently observed that the color tone of the resulting dental composition changes depending upon a kind of a machine used and conditions such as a time for kneading or stirring. This is caused by the uneven dispersion of a pigment or the aggregation of a pigment or the like.
Further, a dental composition containing a large amount of a pigment is used in the dental field, and this is generally referred to as a light-shielding material (opaque material). This composition contains a large amount of a pigment having the strong light-shielding property, such as titanium white or carbon black and, in the case where a crown part of a tooth is defected by dental caries, it is used to remove a metallic color between a metal and a crown material (resin for crown and bridge material), when the defected part of the crown is compensated with a prosthetic crown (crown) combining the metal and the crown material (resin for crown and bridge material). Such a light-shielding material (opaque material) is, for example, a thermal polymerization type comprising a radical polymerizable monomer, an inorganic filler and a peroxide, which is disclosed in JP-A 61-127717 and JP-A 61-152715, and a cold curing type containing tributylborane, which is disclosed in J. J Dent. Mater., vol.7, No.1 (p27-32, 1988). However, in these light-shielding materials (opaque materials), since a special equipment is required to heat, an available time for a work to apply on the metal surface is limited, and it takes a time to cure, clinical needs have shifted to a photopolymerization type. JP-A 59-110606 proposes a dental base material comprising a pigment such as zirconium dioxide, tungsten trioxide and titanium dioxide, a polymerizable monomer and a photocatalyst is described, and German Patent No. 3332179C2 proposes a photopolymerizable dental opacifying agent containing a photocatalyst and a mixture of zirconium dioxide and titanium dioxide as a pigment. These light-shielding materials (opaque materials) should have some fluidity and high opacifying effect in order to be applied on the metal surface in an even thickness. Since such materials have a pigment at a high content and the wettability between a pigment and a polymerizable monomer is poor, it is impossible to retain the initial dispersibility simply by mixing with a pigment, resulting in reaggregation. As the result, various problems arise that in the handling, for example, it can not be applied in an even thickness because the fluidity is decreased with time, and that in the physical properties, for example, it can not be polymerized well towards the deep parts because the light transmittance is decreased. In addition, since a pigment particle is small in a particle size, and a specific surface area is large and, therefore, the surface is very active, it is very difficult to disperse uniformly and stabilize such a pigment particle in a dental composition. However, in order to maintain the properties of a dental composition, the uniform dispersion of a pigment is an important factor.
Japanese Patent No. 2661708 proposes a photocurable light-shielding composition containing a pigment having the surface covered with a polymer, Japanese Patent No. 2812508 proposes a light-shielding composition containing a pigment having the surface treated with a titanate coupling agent, and JP-A 10-94552 proposes a dental photocurable opacifying agent containing a cross-linked bead-like polymer incorporating a color pigment. In all of them, aggregation between pigments is prevented to improve the dispersibility of a pigment by treating or covering the surface of the pigment with a polymer or a surface treating agent, or by incorporating a pigment in a bead-like polymer. In addition, since the above modification of the pigment surface does not contact the active surface of a pigment directly withia polymerizable monomer in a composite restorative material, an improvement is made regarding the characteristics of a paste and the polymerizability of a polymerizable monomer. However, even in these modified pigments, the dispersion state is not still insufficient in a dental composition, and the wettability with a polymerizable monomer is poor.
Further, even when the surfaces of these pigments are treated with, for example, a silane coupling agent which is known in the dental field to improve the compatibility with a polymerizable monomer, since the pigment surface is treated or covered with an organic compound, a surface treating agent does not act effectively and, thus, the sufficient surface treatment effect can not be obtained. When these pigments are used in a dental composition, the stable color tone can not be obtained in a toning step and, furthermore, problems arise in the mechanical properties because defects are produced in the vicinity of the interface between a pigment and a matrix in which a polymerizable monomer is cured.
As mentioned above, there is not a pigment which can be used in a step of endowing various dental compositions in the dental field with the color tone and can impart the excellent dispersibility and the stable color developing property thereto. In addition, a pigment has hitherto been used aiming at endowing a dental composition with the color tone, and there is no pigment which contributes to the stability of a paste, the mechanical properties and the optical properties.
An object of the present invention is to provide a inorganic filler which can be utilized in a dental composition such as a crown and bridge material, a filling material, a prosthetic material, an adhesive material and the like in the dental field, and which can impart the excellent wear resistance and the excellent glossiness after polishing to a dental composition without deteriorating properties such as the mechanical strength and the hardness which are required as a dental composition, as well as a process for producing the same.
Another object of the present invention is to provide a multi-functional filler which can be used in a dental composition such as crown and bridge material, a filling material, a prosthetic material, an adhesive material and the like in the dental field, and which can provide a dental compositon with the excellent color adaptation based on the diffusivity to the incident light and the excellent sustained fluoride releasablity without deteriorating the properties required for a dental material, such as the mechanical strength and the hardness, and a process for producing the same.
Another object of the present invention is to provide an organic compound filler which is usable in a dental composition in the dental field such as a crown and bridge material, a filling material, a prosthetic material, an adhesive material and the like, and which can impart the excellent mechanical strength, the excellent durability and the excellent stable handling as a paste without deteriorating properties such as the polishability, the surface smoothness and glossiness after polishing required as filling material, and a process for producing the same.
Another object of the present invention is to provide a modified filler which can be employed for a dental composition such as a crown and bridge material, a filling material, a prosthesis material, an adhesive material and the like in the dental field, and which maintains the excellent polishability and the excellent optical property such as the surface smoothness and glossiness required as a filling material and, at the same time, can impart the mechanical strength, the wear resistance and the coloring resistance as well as a process for producing the same.
Another object of the present invention is to provide a coloring filler which have so excellent properties in dispersion and color development as to impart the color tone to a dental composition such as a crown and bridge material, a filling material, a prosthetic material, an adhesive material, a light-shielding material (an opaquematerial) and the like in the dental field, and which can impart the excellent paste stability, the excellent mechanical properties and the excellent optical properties thereto.
Further object of the present invention is to provide a process for producing a coloring filler and a dental composition containing the same.
In the first aspect, the present invention relates to an inorganic filler which comprises an inorganic fine particle having an average particle size of 0.01xcx9c5 xcexcm, the inorganic fine particle having the surface covered with polysiloxane.
Also, the present invention relates to a process for producing the aforementioned inorganic filler, which comprises:
(1) a wet-grinding step of fine-grinding a raw material inorganic particle into inorganic fine particles having an average particle size of 0.01xcx9c5 xcexcm; and
(2) a step of forming a polysiloxane film on the surface of the resulting inorganic fine particle.
More particularly, the present invention relates to a process for producing the aforementioned inorganic filler, wherein said step of forming a polysiloxane film comprises:
(2-1) a step of hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I): 
wherein, Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are an integer of 0 to 4, provided that n+m+L=4,
(a combination of two or more of said silane compound may be used) in the presence of the inorganic fine particle dispersed in an aqueous medium, then condensing the resulting silanol compound;
(2-2) a step of drying the resulting aqueous dispersion; and
(2-3) a step of disintegrating the dried material to an average particle size of 0.01xcx9c5 xcexcm.
In addition, the present invention relates to a dental composition comprising the aforementioned inorganic filler in the state in which the surface thereof has been treated with an organosilane compound.
According to the first aspect of the present invention, the following various effects are exerted:
(1) A fine and uniform inorganic filler can be obtained and, since the filler has been covered with polysiloxane without any aggregation, it can be dispersed in a composition in the state of a fine particle having a particle size of 0.01xcx9c5 xcexcm without any secondary aggregation and, thereby, the excellent optical properties and polishability which are characteristic of the fine particle filler can be retained.
(2) Since an inorganic filler is covered with polysiloxane, the conventional silane coupling agent can effectively act on the inorganic filler, and the inorganic filler can be uniformly dispersed in a matrix composed mainly of an organic polymer material. For this reason, in spite of a filler having a fine particle size, the strength and the wear resistance of a composition can be improved.
In the second aspect, the present invention relates to a multi-functional filler, comprising an inorganic particle containing an acid reactive element, wherein a cement reactive phase is formed on the surface of the inorganic particle, and the cement reactive phase is further covered with polysiloxane.
The present invention also relates to a multi-flnctional filler wherein the inorganic particle is a glass.
The present invention further relates to a multi-functional filler wherein the inorganic particle is a fluoride-containing glass.
The present invention additionally relates to a process for producing the above multi-functional filler, which comprises: reacting an acidic polymer with an acid reactive element-containing inorganic fine particle covered with polysiloxane (hereinafter abbreviated to as xe2x80x9ca polysiloxane-covered inorganic fine particlexe2x80x9d).
More specifically, the present invention relates to a process for producing the above multi-functional filler, wherein an acid reactive element-containing inorganic fine particle covered with polysiloxane is obtained by hydrolyzing or partially hydrolyzing, in an aqueous dispersion containing the acid reactive element-containing inorganic fine particle, a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are an integer of 0 to 4, provided that n+m+L=4, and then condensing the obtained silanol compound.
Further, the present invention relates to a process for producing the above multi-functional filler, wherein an acid reactive element-containing inorganic particle covered with polysiloxane is obtained by condensing a low-condensed silane compound obtained by partially hydrolyzing, in an aqueous dispersion containing the acid reactive element-containing inorganic fine particle, a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are an integer of 0 to 4, provided that n+m+L=4, followed by partial condensation.
Still further, the present invention relates to a dental composition comprising any of the above multi-functional fillers in the state where the surface is treated with an organosilane compound represented by the general formula. (II): 
wherein Z is R1Oxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R1 is an organic group having a carbon number of 8 or less, R2 is an organic group, p is an integer of 1xcx9c to 3, and a, b and c are an integer of 0 to 3, provided that a+b+c+p=4.
Particularly, the present invention relates to a dental composition comprising (a) any of the above multi-functional fillers, (b) a polymerizable monomer, and (c) a polymerization initiator.
According to the second aspect of the present invention, the following effects are exerted:
(1) The multi-functional filler of the present invention is characterized in that the light hittered against the present filler is diffused in a wide range of an angle because the filler has a three-layered structure in which the cement reactive phase is formed on the surface of the core inorganic fine particle, and the outside thereof is further covered with polysiloxane. Thus, in a dental composition having the present multi-functional filler incorporated therein, since the incident light can uniformly diffuse towards any direction, the dependency of the colortone on an observation angle is small and, consequently, the same color intended can be observed in any direction after the dental composition is filled in teeth; and
(2) Since the cement reactive phase of the present multi-functional filler is porous, the sustained fluoride releasability can be imparted to a dental composition comprising the multi-functional filler of the present invention by using a fluoride-containing glass as an inorganic fine particle constituting the core.
In order to accomplish the above object, the present inventors studied intensively, and as a result, solved the above problem by providing an organic compound filler comprising an organic-inorganic polymer particle or an organic polymer particle having the surface covered with an inorganic film. That is, the inventors provide the following inventions in this application.
In the third aspect, the present invention provides an organic compound filler, which comprises an organic-inorganic polymer particle or an organic polymer particle, wherein the surface of the organic-inorganic polymer particle or the organic polymer particle is covered with an inorganic film, wherein the inorganic film is a condensate obtained by hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is OH xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are an integer of 0xcx9c to 4, provided that n+m+L=4, and/or a low-condensate of the silane compound.
The present invention also provides an organic compound filler, wherein the inorganic film is a co-condensate obtained by hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I) and/or the low-condensate of the silane compound in the presence of an 20 organosilane compound represented by the general formula (II): 
wherein Z is R1Oxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R1 is an organic group having a carbon number of 8 or less, R2 is an organic group, a, b and c are an integer of 0xcx9c to 3, and p is an integer of 1xcx9c to 3, provided that a+b+c+p=4, and/or a low-condensate of the organosilane compound.
In addition, the present invention provides an organic compound filler, wherein the inorganic film is a co-condensate obtained by hydrolyzing or partially hydrolyzing the silane compound represented by the general formula (I) and/or the low-condensate of the silane compound in the presence of a metal compound.
Further, the present invention provides an organic compound filler, wherein the inorganic film is a co-condensate obtained by hydrolyzing or partially hydrolyzing the silane comrpound represented by the general formula (I) and/or the low-condensate of the silane compound in the presence of the organosilane compound represented by the general formula (II) and/or the low-condensate of the organosilane compound and a metal compound.
Still further, the present invention provides a process for producing the above organic compound filler, which comprises: a step of preparing a dispersion by dispersing an organic-inorganic polymer particle or an organic polymer particle in an aqueous medium, a step of forming an inorganic film on the surface of the particle in the resulting dispersion, a step of separating and/or heat-treating the particle having the inorganic film formed thereon, and a step of disintegrating the heat-treated granule to primary particles.
More specifically, the present invention provides a process for producing the organic compound filler, wherein the step of forming an inorganic film comprises: hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, im and L are an integer of 0xcx9c to 4, provided that n+m+L=4, and/or a low-condensate of the silane compound in the presence of an organic-inorganic polymer particle or an organic polymer particle dispersed in an aqueous medium, followed by condensing; or hydrolyzing or partially hydrolyzing the silane compound represented by the general formula (I) and/or the low-condensate of the silane compound in the presence of at least one of an organosilane compound represented bythe general formula (II): 
wherein Z is R1Oxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R1 is an organic group having a carbon number of 8 or less, R2 is an organic group, a, b and c are an integer of 0xcx9c to 3, and p is an integer of 1xcx9c to 3, provided that a+b+c+p=4, a low-condensate of the organosilane compound and a metal compound, followed by co-condensing.
Finally, the present invention provides a dental composition comprising (a) an organic compound filler of the present invention, (b) a polymerizable monomer, and (c) a polymerization initiator.
According to the third aspect of the present invention, the following effects are exerted by covering the surface of the organic-inorganic polymer particle or an organic polymer particle with an inorganic film.
(1) Since the surface of the conventional organic-inorganic polymer particle or organic polymer particle has a little amount of an inorganic component and almost all components on the surface is an organic component, a surface treating agent such as a silane coupling agent can not act effectively and, to the contrary, since the present organic compound filler is covered with an inorganic film, a surface treating agent such as a silane coupling agent can act effectively to disperse uniformly in a resin matrix.
(2) When the organic compound filler of the present invention is used in a dental composition as a filler, it can impart the excellent polishability, particularly the surface smootlness and glossiness after polishing, as well as the excellent mechanical properties and the excellent durability, and the excellent stable paste handling.
(3) In addition, by incorporating a heavy metal element into the covering inorganic film, the radiopacity can be additionally impartred.
In order to accomplish the above object, the present inventors studied intensively and, as a result, solved the problems by providing a modified filler in which the surface of an inorganic fine particle having an average particle size of 0.01xcx9c5 xcexcm is covered with polyorganosiloxane. That is, the present inventors provide the following invention in this application.
In the fourth aspect, the present invention provides a modified filler which comprises an inorganic fine particle having an average particle size of 0.01xcx9c5 xcexcm and having the surface covered with polyorganosiloxane, said polyorganosiloxane is a co-condensate -obtained by hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are all an integer of 0xcx9c to 4, provided that m+n+L=4, and/or a low-condensate of the silane compound and an organosilane compound represented by the general formula (II): 
wherein Z is R1Oxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R1 is an organic group having a carbon number of 8 or less, R2 is an organic group, p is an integer of 1 to 3, and a, b and c are all an integer of 0xcx9c to 3, provided that a+b+c+p=4, and/or a low-condensate of the organosilane compound.
Further, the present invention provides a modified filler in which the polyorganosiloxane is a co-condensate obtained by hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I) and/or a low-condensate of the silane compound and an organosilane compound represented by the general formula (II) and/or a low-condensate of the organosilane compound in the presence of a metal compound.
In addition, the present invention provides a process for producing the above-mentioned modified filler which comprises (1) a wet-grinding step of fine-grinding a raw material inorganic particle into inorganic particles having an average particle size of 0.01xcx9c5 xcexcm, or a wet-dispersion step of disintegrating an aggregated inorganic particle into primary particles, the primary particle having an average particle size of 0.01xcx9c5 xcexcm, and (2) a step of forming a polyorganosiloxane film on the surface of the resulting inorganic fine particle.
More particularly, the present invention provides a process for producing the above-mentioned modified filler in which the step of forming a polyorganosiloxane film comprises (2-1) a step of hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are an integer of 0xcx9c to 4, provided that n+m+L=4, and/or a low co-condensate of the silane compound and an organosilane compound represented by the general formula (II): 
wherein Z is R1Oxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R1 is an organic group having a carbon number of 8 or less, R2 is an organic group, p is an integer of 1xcexc to 3, and a, b and c are all an integer of 0xcx9c to 3, provided that a+b+c+p=4, and/or a low co-condensate of the organosilane compound, and co-condensing the resulting silanol compound, or
a step of hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I) and/or a low-condensate of the silane compound and an organosilane compound represented by the general formula (II) and/or a low-condensate of the organosilane compound in the presence of a metal compound and, then, co-condensing the silanol compound, (2-2) a step of heat-treating the resulting aqueous dispersion, and (2-3) a step of disintegrating the heat-treated solidified material to an average particle size of 0.01xcx9c5 xcexcm.
Furthermore, the present invention provides a dental composition which comprises (a) the aforementioned modified filler, (b) a polymerizable monomer, and (c) a polymerization initiator.
According to the fourth aspect of the aforementioned present inventions, the following effects are exerted.
(1) By forming a polyorganosiloxane film on the surface of an inorganic fine particle which was fine-ground by fine-grinding or dispersion techniques, a modified filler can be obtained in the state of a fine particle of 0.01xcx9c5 xcexcm without secondary aggregation.
(2) The resulting fine and uniform modified filler can be dispersed in a dental composition in the state of a primary particle without secondary aggregation and the optical properties such as the excellent polishability and the surface smoothness of a fine particle filler are retained. In addition, this polyorganosiloxane film reforms only the surface of an inorganic fine particle and the properties originally harbored by an inorganic fine particle are maintained.
(3) Since a modified filler is covered with polyorganosiloxane, an organosilane compound such as a silane coupling agent which has previously been used can effectively exert its action irrespective of a kind of an inorganic fine particle and the wettability with a resin matrix can be further improved. Such a modified filler is dispersed in a dental composition more uniformly and, together with the effect of formation of a polyorganosiloxane film, the mechanical strength and the wear resistance can be improved in spite of a fine filler.
In order to accomplish the above object, the present inventors studied intensively and, as a result, found that by covering the surfaces of an inorganic particle and a coloring particle with poly(organo)siloxane in the state where both particles were mixed and dispersed uniformly, a coloring filler in which a coloring particle is fixed in the state of a primary particle and is uniformly dispersed can be provided, which resulted in the solution of the above problems.
That is, we provide the following inventions in this application.
In the fifth aspect, the present invention provides a dental coloring filler, which comprises an inorganic particle and a coloring particle, wherein the inorganic particle and the coloring particle are uniformly mixed and dispersed, the surfaces of these particles are covered with poly(organo)siloxane, and poly(organo)siloxane is a condensate obtained by hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are an integer of 0xcx9c to 4; provided that n+m+L=4, and/or a low-condensate of the silane compound.
The present invention also provides a dental coloring filler, wherein poly(organo)siloxane is a co-condensate obtained by hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I) and/or a low-condensate of the silane compound in the presence of an organosilane compound represented by the general formula (II): 
wherein Z is R1Oxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R1 is an organic group having a carbon number of 8 or less, R2 is an organic group, p is an integer of 1xcx9c to 3, and a, b and c are an integer of 0xcx9c to 3, provided that a+b+c+p=4, and/or a low-condensate of the organosilane compound.
In addition, the present invention provides a dental coloring filler, wherein poly(organo)siloxane is a co-condensate obtained by hydrolyzing or partially hydrolyzing the silane compound represented by the general formula (I) and/or the low-condensate of the silane compound in the presence of a metal compound.
Further, the present invention provides a dental coloring filler, wherein poly(organo)siloxane is a co-condensate obtained by hydrolyzing or partially hydrolyzing the silane compound represented by the general formula (I) and/or the low-condensate of the silane compound in the presence of the organosilane compound represented by the general formula (II) and/or the low-condensate of the organosilane compound and a metal compound.
Still further, the present invention provides a process for producing the above dental coloring filler, which comprises (1) a step of preparing a mixed particle by uniformly mixing and dispersing an inorganic particle and a coloring particle, and (2) a step of forming a poly(organo)siloxane film on the surface of the resulting mixed particle.
More specifically, the present invention provides a process for producing a dental coloring filler, wherein the step of forming a poly(organo)siloxane film comprises:
in the presence of a mixed particle which is uniformly niixed and dispersed, hydrolyzing or partially hydrolyzing a silane compound represented by the general formula (I): 
wherein Z is ROxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R is an organic group having a carbon number of 8 or less, and n, m and L are an integer of 0xcx9c to 4, provided that n+m+L=4, and/or a low-condensate of the silane compound, followed by condensing; or
in the presence of a mixed particle which is uniformly mixed and dispersed, hydrolyzing or partially hydrolyzing the silane compound represented by the general formula (I) and/or the low-condensate of the silane compound in the presence of at least one of an organosilane compound represented by the general formula (II): 
wherein Z is R1Oxe2x80x94 or OCNxe2x80x94, X is halogen, Y is xe2x80x94OH, R1 is an organic group having a carbon number of 8 or less, R2 is an organic group, p is an integer of 1xcx9c to 3, and a, b and c are an integer of 0xcexc to 3, provided that a+b+c+p=4, a low-condensate of the organosilane compound and a metal compound, followed by co-condensing.
Finally, the present invention provides a dental composition, which comprises (a) a dental coloring filler of the present invention, (b) a polynernzable monomer and (c) a polymerization initiator.
Furthermore, the present invention provides a dental composition further comprising (d) a filler.
According to the fifth aspect of the present invention, following effects are exerted.
(1) In the coloring filler of the present invention, an inorganic particle and a coloring particle are mixed and dispersed uniformly, and the surfaces of these particles are covered with poly(organo)siloxane. Since the coloring particle is fixed in the state of a primary particle by the poly(organ)siloxane film, it does not aggregate and, therefore, it is excellent in color development as well as in dispersibility in a dental composition.
(2) Generally, a dental composition is endowed with the color tone by using a diluted pigment in which a pigment is diluted in advance. However, since in the present coloring filler, an inorganic particle and a coloring particle have been already dispersed uniformly, a step of preparing a diluted pigment is not required and, further, the pigment concentration can be freely adjusted. The toning by using the present coloring filler allows for clear and abundant colors as requested by clinicians.
(3) Since an inorganic particle and a coloring particle in the present coloring filler are covered with poly(organo)siloxane, a surface treating agent such as a silane coupling agent which has hitherto been used is possible to act effectively, and the wettability with a resin matrix in a dental composition can be further improved. Such coloring filler can be dispersed more uniformly in a dental composition and, by combining with the effect of forming a poly(organo)siloxane film, the coloring filler endows a dental composition with the color tone and, additionally, can contributes to, for example, the mechanical properties, the optical properties and the stability of the paste characteristics.